Non-impact recording, or the ink jet method of recording, is becoming a popular method for converting image data in the form of electrical signals into hard copies because it produces less noise during recording than does impact printing. The ink jet method is also useful because it operates with ordinary paper without the need for a special process, such as fixing, in order to produce a permanent record.
The ink jet method that has already been put to practical use involves filling an airtight container with ink, applying a pressure pulse to the container, and sending the ink out of an orifice of the container in a jet for recording purposes. The ink jet apparatus used in such method, however, cannot be made compact due to its operating mechanism. The apparatus also requires mechanical scanning to record at a desired image density, which causes the recording speed to be reduced.
At the same time, there have been proposed techniques for remedying shortcomings inherent in the ink jet method and making high-speed recording possible. The magnetic ink jet method is a typical example of such improvement and is accomplished by providing magnetic ink close to a magnetic electrode array, forming an ink-jet state corresponding in position to a picture element by making use of a swell of the ink in the presence of a magnetic field, and jetting the magnetic ink in the presence of a static electric field. Since this method admits of electronic scanning, high-speed recording becomes possible, however, the selection of ink and coloration characteristic of the ink jet method are limited.
In addition to the aforesaid methods, the so-called plane ink jet method is also well known. This method, involves arranging ink in a slitlike inkholder in parallel to an electrode array, and jetting the ink in accordance with an electric field pattern formed between an electrode facing the electrode array so that ink droplets selectively impact upon an intervening recording paper. Since no minute orifice for storing ink is required in this method, ink clogging can be prevented. However, a high voltage must be applied to jet the ink droplets which makes it necessary to drive the electrode array on a time division basis to prevent a voltage leak across the adjoining or neighboring electrodes. Consequently, the recording speed is limited.
There has also been proposed the so-called heat bubble jet method for jetting ink out of an orifice by means of thermal energy. In this method, the ink is abruptly, locally heated to cause film boiling and a pressure rise resulting from the rapid formation of bubbles within the orifice is utilized to jet the ink. However, the film boiling temperatures are as high as 500.degree.-600.degree. C. and this makes it difficult to put the aforesaid method to practical use because the ink properties tend to change at high temperatures and the protective layer on the heating resistor also deteriorated.
As set forth above, many problems are still present in the ink jet methods heretofore developed. Such problems include limitations on recording speed, the necessity of employing special ink and contriving a particular driving means, and thermal deterioration of the ink and the heating elements.